Actually except for backgrounds and glowing objects an ambient value of zero is appropriate. I just wish Poser modelers would start learning that fact instead of using ambient color and value when they should be using diffuse color and value. I am grateful that the default ambient value in P5 is zero because it allows me to use my lights as they were intended to be used and does not cause that classic "washed-out" look some people get because they use ambient color instead of diffuse color. If you use ambient color when you should be using diffuse color your object will not accept shadows, will not shade properly, and will dilute the effect of your lighting. The exceptions are of course when you WANT an object to glow or be free of interference from shadows (like photo backgrounds.